In that photo, it is the component installed between the inline cable adjuster and the disc caliper. It's called the Brake Power Booster (BPB) made by Sidetrak.
Essentially, it does the same thing as an inline Travel Agent, but also has a couple throw settings you can chose from.
Available from PrecisionTandems (in the "Brakes" section under the heading "
TRAVEL AGENTS - V-DAPTORS - Brake Power Boosters - BPB") and perhaps others too.